Frequency Uncertainty Research Articles

Signal-to-noise ratio enhancement using block-matching and 3D filtering for both Brillouin gain and phase spectra in sweep-free Brillouin optical time-domain analyzer

Conventional Brillouin optical time-domain analyzer (BOTDA) requires the process of frequency scanning, which is very time-consuming. The data acquisition speed of the conventional BOTDA is too slow to realize dynamic sensing. The use of the optical frequency comb-based BOTDA can avoid the frequency scanning and speed up the measurement. But, to achieve dynamic measurement, it is also necessary to reduce the time for signal averaging to further improve the measurement speed. However, few averaging times lead to poor signal-to-noise ratio (SNR), which will limit the sensing performance of the system. Block-matching and 3D filtering (BM3D) algorithm is proposed to achieve the denoising of sensing signals in the sweep-free BOTDA using intensity-modulated direct-detection optical orthogonal frequency division multiplexing. The impact of the BM3D parameters on the denoising performance is analyzed, which is used to realize parameter optimization. To demonstrate the denoising performance of BM3D under different noise levels, white Gaussian noise with different standard deviation (STD) is added to the original sensing signal. When the STD of the added noise is 0.07 mV, the SNR after denoising using optimized BM3D is improved by 9.7 dB for the Brillouin gain spectrum (BGS) and 10.6 dB for the Brillouin phase spectrum (BPS), respectively, and the frequency uncertainty is reduced to be below 1 MHz. For a wide range of noise levels, BM3D has shown excellent denoising performance, and the average SNR after denoising is improved to be 16.8 and 15.6 dB for BGS and BPS, respectively, and the corresponding frequency uncertainty is reduced to be below 1.2 MHz.

Evaluation of the blackbody radiation shift of an Yb optical lattice clock at KRISS

As optical clocks are improved to reach the frequency uncertainty below the 10−17 level, the frequency shift due to the blackbody radiation (BBR) has been one of the major systematic effects hindering further improvement. To evaluate the BBR shift of an Yb optical lattice clock at KRISS, we installed an in-vacuum BBR shield and made radiation thermometry using a black-coated-sphere thermal probe. After we quantitatively measured the conduction loss of the thermal probe and the effects of all the external radiation sources, we determined the temperature at the atom trap site with an uncertainty of 13 mK, which corresponds to an uncertainty of 0.22 mHz in the clock frequency (a fractional frequency of 4.2 × 10−19). The total uncertainty of the BBR shift including the atomic response is 9.5 × 10−19.

Multiple tuned mass damper control of vortex-induced vibration in bridges based on failure probability

The multiple tuned mass damper (MTMD) is used instead of the single tuned mass damper (STMD) in this paper to improve the robustness in the mitigation of the vortex-induced vibration (VIV) in bridges. A framework of the parameter design of the MTMD mitigating the VIV is proposed based on a failure probability, which is derived as the objective function of the MTMD control by considering the uncertainties in bridge, aerodynamic, and MTMD parameters. Furthermore, a flowchart of the parameter optimization of the MTMD is presented by considering the failure probability and stroke limitation, simultaneously. At last, a numerical example of a box girder continuous bridge equipped with the optimized MTMD under the VIV is presented. Results show that the uncertainties in aerodynamic parameters characterizing the occurring condition and intensity of the VIV have great influence on the negative damping ratio induced by the VIV, while the uncertainties in natural frequencies of the bridge and MTMD have great influence on the equivalent damping ratio contributed by the MTMD. The superiority of the MTMD in the robustness will be lost if the intensity of the VIV is weak, but the MTMD is more robust than the STMD if the intensity of the VIV is modest or strong. The failure probability of the MTMD is 30 %∼50 % of that of the STMD when the total mass ratio is 0.6 %.

High spatial resolution fast Brillouin optical time-domain analysis enabled by frequency-agility digital optical frequency comb.

A significant spatial resolution enhancement scheme for digital optical frequency comb (DOFC)-based fast Brillouin optical time-domain analysis (BOTDA) is proposed and experimentally demonstrated by using frequency-agility probes, without sacrificing the frequency resolution. The proposed system ensures high spatial resolution by using short frame duration, meanwhile enabling high frequency resolution retrieval of the Brillouin gain spectrum using frequency interleaving of multiple frequency-agility DOFC probes. Additionally, quadratic phase coding is introduced to release the influence of the high peak to average power ratio of the probes. Eventually, the proposed BOTDA sensor achieves a record 5-m spatial resolution over 10-km fiber with less than 2-MHz frequency uncertainty, and a 1-GHz dynamic measurement range. For proof of concept, 10-Hz vibration sensing is also successfully demonstrated at a 40-Hz sampling rate, showing great potential for fast measurement. It is worth mentioning that a higher spatial resolution can be achieved by using more frequency-agility DOFC probes, albeit at the expense of increasing the measurement time.

Continuous IPPP links for UTC

The technique of precise point positioning with integer ambiguity resolution (IPPP) has been developed for many years and has been shown to significantly improve the long-term performance of time and frequency transfer with respect to other GNSS-based techniques. In this paper, we present results of GPS IPPP links over a period of 22 months for a dozen time laboratories participating to UTC. We show that continuous links, in which the continuity of the GPS phase measurements is preserved, can be maintained for periods exceeding one year and further extended if data from two receivers per station are available. We quantify the frequency transfer uncertainty of IPPP by comparison to optical links and show how IPPP could improve UTC links to below 1 × 10−16 relative frequency uncertainty over averaging times of up to one month, i.e. the characteristic period of UTC publication. Comparisons of primary and secondary frequency standards reported for TAI indicate that IPPP could somewhat improve the accuracy of TAI/UTC. Comparisons of IPPP to two-way time transfer techniques reveal very long-term ns-size instabilities which must be further studied. Use of IPPP for UTC links is possible only if integer GNSS satellite products become available with a short delay and we report on such experimental products. Finally, we discuss the practical implications of using IPPP link in UTC and describe how the necessary steps could be implemented.

Robust fault detection and isolation for dynamics of high-speed train with uncertainties based on descriptor systems

This paper proposes a new type of robust fault detection and isolation filter for dynamics of HST based on descriptor systems with uncertainties in finite frequency. This filter is designed based on the unknown input filter to decouple the non-linear variables due to the aerodynamic drag pressing on the trains. The exogenous disturbance is partitioned into two parts-the decoupling one is regarded as the augmented variables of the non-linear part of the systems, and the non-decoupling one is seen as the augmented disturbance along with the uncertainties. Concurrent faults of different positions are considered, residual evaluation functions and adaptive threshold are given to judge if the faults occur. Fault isolation is implemented by a set of detection subspaces associated with every different fault which is assigned to its own detection subspace. The residual is not only sensitive to the fault, but also has a robustness against the non-decoupling disturbance and uncertainties in finite frequency. Simulation examples are given to demonstrate the effectiveness of this method.

A Bayesian copula-based nonstationary framework for compound flood risk assessment along US coastlines

• Trends in and dependence between sea level and precipitation increase the probability of compound flooding along US coastlines, most notably along the Southeast coast. • A Bayesian copula-based framework captures the uncertainty in the quantification of compound flood frequency. • Precipitation trends play a major role in increasing the uncertainty in compound flood frequency. • To account for non-stationarity, a long historical record is required. When elevated coastal water levels and heavy precipitation occur simultaneously or in succession, their joint impact may be exacerbated compared to their individual occurrence. Sea-level rise, shifts in precipitation patterns, and the presence of correlation between flooding drivers can increase the frequency of these compound events. In this study, a copula-based Bayesian framework that incorporates the impact of dependence between flooding drivers (i.e., sea level and precipitation) and accounts for the nonstationarity in these hydrologic variables is developed. The framework is used to assess how the individual and combined effects of dependence and nonstationarity influence the frequency and magnitude of compound coastal-pluvial flooding. Furthermore, the Bayesian framework allows for the incorporation of uncertainty, which may arise from shortage of data, model selection, and parameter estimation, into flood frequency analysis. The proposed framework is applied to 32 station pairs across the US coastlines to identify locations that experience the highest risk of compound flooding and to assess the major contributors to uncertainty in the bivariate return period. The results show that the Southeast Atlantic coast experiences the highest increase in the risk of compound flooding, followed by the Gulf and Northeast Atlantic coasts. Sea-level rise and dependence between flooding drivers have a larger influence on bivariate return periods than changes in precipitation patterns. Under a nonstationary framework, precipitation is the major contributor to uncertainty compared to sea level and dependence. In addition, results demonstrate that uncertainty is highly dependent on the length of joint data. This study highlights the importance of incorporating hydrological dependence and trends and associated uncertainty into the quantification of return periods to permit reliable estimation of flood hazards.

Global Flash Drought Analysis: Uncertainties From Indicators and Datasets

AbstractFlash Drought (FD) has garnered much attention in recent years, with significant advancements in the indicators applied for identifying these rapidly intensifying events. However, the difference in existing FD definitions and methodologies among research communities and the choice of different data sources underscores the importance of addressing the uncertainties associated with the global FD characteristics and their drivers. This study compares two key FD indicators derived based on evaporative stress ratio (ESR) and root‐zone soil‐moisture (RZSM) using three different data sources to investigate the uncertainties in global FD frequency and intensity (speed), and the influencing drivers. The results suggest that such disparities are significant in the two FD indicators across different climate regions of the globe. The results highlight varying spatial drivers of FD frequency, intensity, and their evolution, potentially linked to background aridity. Changes in precipitation, temperature, vapor pressure deficit, and soil‐temperature coupling play an important role with a cascading (concurrent) impact on the evolution of FD based on RZSM (ESR). The relationship between ESR and RZSM fails to explain most of the variance in each of these indicators specific to the FD episodes, especially in the transitional and humid climate regimes. Overall, the results highlight the necessity of more nuanced methodologies for deriving FD indicators that can efficiently couple the rapid soil‐moisture depletion rates in deeper layers with changes in atmospheric evaporative demand which has direct implications on vegetation health.

Aquifer heterogeneity controls to quality monitoring network performance for the protection of groundwater production wells

A groundwater monitoring network surrounding a pumping well (such as a public water supply) allows for early contaminant detection and mitigation where possible contaminant source locations are often unknown. This numerical study investigates how the contaminant detection probability of a hypothetical sentinel-well monitoring network consisting of one to four monitoring wells is affected by aquifer spatial heterogeneity and dispersion characteristics, where the contaminant source location is randomized. This is achieved through a stochastic framework using a Monte Carlo approach. A single production well is considered that results in converging non-uniform flow close to the well. Optimal network arrangements are obtained by maximizing a weighted risk function that considers true and false positive detection rates, sampling frequency, early detection, and contaminant travel time uncertainty. Aquifer dispersivity is found to be the dominant parameter for the quantification of network performance. For the range of parameters considered, a single monitoring well screening the full aquifer thickness is expected to correctly and timely identify at least 12% of all incidents resulting in contaminants reaching the production well. This proportion increases to a global maximum of 96% for a network consisting of four wells and very dispersive transport conditions. Irrespective of network size and sampling frequency, more dispersive transport conditions result in higher detection rates. Increasing aquifer heterogeneity and decreasing aquifer spatial continuity also lead to higher detection rates, though these effects are diminished for networks of 3 or more wells. Statistical anisotropy has no effect on the network performance. Earlier detection, which is critical for remedial action and supply safety, comes with a significant cost in terms of detection rate, and should be carefully considered when a monitoring network is being designed.

Two-Time Procedure for Calculation of Carrier Frequency of Phasomodulated in Communication Systems

The use in radio communication systems of phase modulation of a signal intended for the transmission of useful information in a continuous mode creates the problem of frequency uncertainty of the received signal by frequency.In practice, it is not possible to implement frequency estimation in the conditions of chat uncertainty of the signal in the channel with low energy of the signal received in the continuous mode. Therefore, the estimation of the carrier frequency offset of the signal received relative to the nominal value is carried out before other synchronization procedures are included, namely: phase synchronization and clock synchronization. The paper generalizes the procedure and forms a two-step procedure for calculating the carrier frequency of the phase-modulated signal of a radio communication system for data transmission in a continuous mode, taking into account the condition of uncertainty of all signal parameters. Achieving the minimum observation interval in the given order of calculation of the carrier frequency is ensured by the use of the fast Fourier transform function. In order to analyze the effectiveness of this procedure, the process of estimating the carrier frequency of the phase-modulated signal of the radio communication system during data transmission in continuous mode and functional dependences of the maximum frequency in the signal spectrum and the minimum variance of carrier frequency estimation. This procedure allows a two-stage assessment of the carrier frequency according to the rule of maximum likelihood, taking into account the condition of uncertainty of all parameters of the signal received by the satellite communication system in a continuous mode with a minimum observation interval. Achieving the minimum observation interval in the given order of carrier frequency estimation is ensured by using the fast Fourier transform function and two estimation steps. The analysis of the efficiency of the estimation of the specified order was carried out on the basis of comparison of a ratio of the received minimum variance of an estimation of a carrier frequency and theoretically possible border of the minimum variance.

Impact of the COVID‐19 Economic Downturn on Tropospheric Ozone Trends: An Uncertainty Weighted Data Synthesis for Quantifying Regional Anomalies Above Western North America and Europe

This study quantifies the association between the COVID‐19 economic downturn and 2020 tropospheric ozone anomalies above Europe and western North America, and their impact on long‐term trends. Anomaly detection for an atmospheric time series is usually carried out by identifying potentially aberrant data points relative to climatological values. However, detecting ozone anomalies from sparsely sampled ozonesonde profiles (once per week at most sites) is challenging due to ozone's high temporal variability. We first demonstrate the challenges for summarizing regional trends based on independent time series from multiple nearby ozone profiling stations. We then propose a novel regional‐scale anomaly detection framework based on generalized additive mixed models, which accounts for the sampling frequency and inherent data uncertainty associated with each vertical profile data set, measured by ozonesondes, lidar or commercial aircraft. This method produces a long‐term monthly time series with high vertical resolution that reports ozone anomalies from the surface to the middle‐stratosphere under a unified framework, which can be used to quantify the regional‐scale ozone anomalies during the COVID‐19 economic downturn. By incorporating extensive commercial aircraft data and frequently sampled ozonesonde profiles above Europe, we show that the complex interannual variability of ozone can be adequately captured by our modeling approach. The results show that free tropospheric ozone negative anomalies in 2020 are the most profound since the benchmark year of 1994 for both Europe and western North America, and positive trends over 1994–2019 are diminished in both regions by the 2020 anomalies.

Distributed Optical Fiber Sensing System for Large Infrastructure Temperature Monitoring

In this article, a distributed optical fiber sensing system for large infrastructure temperature monitoring is proposed. To meet the requirements of monitoring networks in terms of measurement accuracy, spatial resolution, and real-time or quasireal-time performance, a quaternion wavelet transform (QWT) image denoising algorithm is proposed to address the original edge node data for the structural monitoring networks of large infrastructures. A distributed Brillouin optical time-domain analysis (BOTDA) sensing system with a 40-km sensing fiber is established. The raw Brillouin gain spectrum (BGS) image is decomposed into one magnitude image and three phase images by QWT. The phase images of the OWT are distributed randomly and disorderly with respect to the noise, while the magnitude image of the quaternion wavelet is greatly affected by the noise. The useful message energy of the magnitude image is concentrated on a small number of coefficients with large amplitude, while the noise mainly corresponds to the coefficients with smaller amplitude. Then, the Bayes shrink threshold method is introduced to filter out noise in the magnitude image. The results indicate that the signal-to-noise ratio (SNR) and the frequency uncertainty have been improved significantly. The accuracy of the retrieved Brillouin frequency shift from denoised BGS images reaches 0.2 MHz, which corresponds to a temperature error of ±0.1 °C. Less than 4 s are required to process a BGS image with 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 40 000 pixels by the QWT denoising technique. The uploaded data obtained from 40 M bytes of raw data are reduced to 0.08 M bytes for each measurement. We hope that with technological progress and algorithm optimization, the distributed optical fiber sensing system based on the QWT image denoising algorithm will have an important role in the real-time application of large-scale infrastructure structural health monitoring for the Internet of Things.

A three-stage automated modal identification framework for bridge parameters based on frequency uncertainty and density clustering

As the automated modal analysis is crucial for a continuous monitoring system, this study proposes a framework for automated modal identification of bridge parameters based on the uncertainty of estimated frequencies and density-based clustering algorithm, which consists of the following three stages: First, the modal parameters and standard deviations of the estimated frequencies are calculated in a wide range of model orders to construct the stabilization diagram using the reference-based covariance-driven stochastic subspace identification algorithm. Second, the criteria of frequency uncertainty and stabilization are adopted to eliminate the spurious modes. Third, for present purpose, the modified version of an unsupervised density-based clustering algorithm is introduced to group physical modes and detect outliers to reach automated identification of bridge modal parameters. From the analysis, it has shown that the proposed framework is powerful in eliminating the spurious modes and robust in the presence of interference caused by spurious modes while a simple procedure for clustering physical modes with desired statistical reliability is employed.

The periodically extended stiffness nonlinear energy sink

Conventional nonlinear energy sinks (NES) are considered to be a more robust alternative to linear vibration absorbers such as the tuned-mass–damper (TMD). While the conventional NES has a larger efficient frequency bandwidth than the TMD, it is only really efficient for a small energy range. This implies a deterioration of the NES’s mitigation properties if the primary system’s amplitude varies. To overcome this issue, other researchers resort to increasing the complexity of the NES by adding degrees-of-freedom. Here, another line of thought is presented, by proposing an unconventional stiffness characteristic. To increase the energy bandwidth the NES in this paper features a non-smooth, periodically extended stiffness characteristic. This NES is attached to an uncertain primary system and its performance is compared with that of the conventional NES and of the TMD by deriving the slow invariant manifolds (SIMs) in transient 1:1 resonance. The SIMs are curves that relate the vibration amplitudes of the primary system and the NES, and serve as an easy and computationally efficient tool to analyze performance. The research in this paper will prove that the newly proposed NES can be both robust regarding energy and frequency uncertainty, by considering the novel periodically extended stiffness characteristic.

Active Frequency Measurement on Superradiant Strontium Clock Transitions.

We develop a stochastic mean-field theory to describe active frequency measurements of pulsed superradiant emission, studied in a recent experiment with strontium-87 atoms trapped in an optical lattice inside an optical cavity [M. Norcia et al., Phys. Rev. X 8, 021036 (2018)PRXHAE2160-330810.1103/PhysRevX.8.021036]. Our theory reveals the intriguing dynamics of atomic ensembles with multiple transition frequencies, and it reproduces the superradiant beats signal, noisy power spectra, and frequency uncertainty in remarkable agreement with the experiments. Moreover, using longer superradiant pulses of similar strength and shortening the experimental duty cycle, we predict a short-term frequency uncertainty 7×10^{-17}/sqrt[τ/s], which makes active frequency measurements with superradiant transitions comparable with the record performance of current frequency standards [M. Schioppo et al., Nat. Photonics 11, 48 (2017)NPAHBY1749-488510.1038/nphoton.2016.231]. Our theory combines cavity quantum electrodynamics and quantum measurement theory, and it can be readily applied to explore conditional quantum dynamics and describe frequency measurements for other processes such as steady-state superradiance and superradiant Raman lasing.

Two-Time Procedure for Calculation of Carrier Frequency of Phasomodulated in Communication Systems

The use in radio communication systems of phase modulation of a signal intended for the transmission of useful information in a continuous mode creates the problem of frequency uncertainty of the received signal by frequency.In practice, it is not possible to implement frequency estimation in the conditions of chat uncertainty of the signal in the channel with low energy of the signal received in the continuous mode. Therefore, the estimation of the carrier frequency offset of the signal received relative to the nominal value is carried out before other synchronization procedures are included, namely: phase synchronization and clock synchronization. The paper generalizes the procedure and forms a two-step procedure for calculating the carrier frequency of the phase-modulated signal of a radio communication system for data transmission in a continuous mode, taking into account the condition of uncertainty of all signal parameters. Achieving the minimum observation interval in the given order of calculation of the carrier frequency is ensured by the use of the fast Fourier transform function. In order to analyze the effectiveness of this procedure, the process of estimating the carrier frequency of the phase-modulated signal of the radio communication system during data transmission in continuous mode and functional dependences of the maximum frequency in the signal spectrum and the minimum variance of carrier frequency estimation. This procedure allows a two-stage assessment of the carrier frequency according to the rule of maximum likelihood, taking into account the condition of uncertainty of all parameters of the signal received by the satellite communication system in a continuous mode with a minimum observation interval. Achieving the minimum observation interval in the given order of carrier frequency estimation is ensured by using the fast Fourier transform function and two estimation steps. The analysis of the efficiency of the estimation of the specified order was carried out on the basis of comparison of a ratio of the received minimum variance of an estimation of a carrier frequency and theoretically possible border of the minimum variance.

The Application of Low-Frequency Transition in the Assessment of the Second-Order Zeeman Frequency Shift.

Second-order Zeeman frequency shift is one of the major systematic factors affecting the frequency uncertainty performance of cesium atomic fountain clock. Second-order Zeeman frequency shift is calculated by experimentally measuring the central frequency of the (1,1) or (−1,−1) magnetically sensitive Ramsey transition. The low-frequency transition method can be used to measure the magnetic field strength and to predict the central fringe of (1,1) or (−1,−1) magnetically sensitive Ramsey transition. In this paper, we deduce the formula for magnetic field measurement using the low-frequency transition method and measured the magnetic field distribution of 4 cm inside the Ramsey cavity and 32 cm along the flight region experimentally. The result shows that the magnetic field fluctuation is less than 1 nT. The influence of low-frequency pulse signal duration on the accuracy of magnetic field measurement is studied and the optimal low-frequency pulse signal duration is determined. The central fringe of (−1,−1) magnetically sensitive Ramsey transition can be predicted by using a numerical integrating of the magnetic field “map”. Comparing the predicted central fringe with that identified by Ramsey method, the frequency difference between these two is, at most, a fringe width of 0.3. We apply the experimentally measured central frequency of the (−1,−1) Ramsey transition to the Breit-Rabi formula, and the second-order Zeeman frequency shift is calculated as 131.03 × 10−15, with the uncertainty of 0.10 × 10−15.

Clutching inerters enhanced tuned mass dampers for structural response mitigation under impulsive and seismic excitations

Inerters, a type of two-terminal inertial elements, have significantly enhanced the performance of conventional control devices. The clutching inerters are especially appealing since they take energy away from the structural system without transferring back. In this study, a clutching inerter enhanced tuned mass damper (TMDCI) is proposed. First, the formation of the TMDCI is described based on a tuned mass damper inerter and two clutching flywheels. Then, the equations of motion are derived for the TMDCI on a single-degree-of-freedom (SDOF) primary structure. Subsequently, the modal properties of the TMDCI system are revealed by examining the steady-state responses under harmonic ground excitations. Afterward, performance analyses are conducted for the TMDCI on SDOF and three-DOF steel structures when subjected to initial velocities. The frequency robustness and parametric sensitivity of the TMDCI are evaluated on the SDOF structure, whereas practical concerns regarding the hosting location and stiffness demand of the TMDCI are addressed on the three-DOF structure. Finally, the seismic performance of the TMDCI is investigated on the three-DOF structure under a suite of earthquakes. The results show that the TMDCI exhibits a large damping effect which can reduce responses in both the structure and device and maintain strong robustness against frequency uncertainties. This study demonstrates the great potential of TMDCIs as an effective and affordable control strategy for the seismic protection of structures.

Security‐constrained optimal scheduling and operation of island microgrids considering demand response and electric vehicles

As an independent unit, microgrid operator (MGO) should respond to the energy demand of customers with an optimal provision cost. Apart from the ability to guarantee the security of microgrid (MG) operation, the MGO should consider the greenhouse emission effects as well. This paper investigates a novel energy management system for an islanded MG. In the proposed strategy, two efficient methodologies are used to maximize the profit and security of the MG: (a) the optimal operation of electric vehicles (EVs) in vehicle-to-grid (V2G) mode and (b) the use of demand response (DR) program. Besides, a hierarchical control structure is proposed to manage frequency and voltage uncertainties in a permissible range. Improving the reliability of the MG is another goal of the proposed strategy, which is pursued by the studied controlling framework. The proposed approach is evaluated through a set of simulation and GAMS tests. Results indicate that the frequency deviation of the MG is damped through the proposed management strategy and place the spotlight on the effectiveness of the approach.

Time-Scale Decomposition Techniques Used in the Ship Path-Following Problem with Rudder Roll Stabilization Control

The motion control of a surface ship based on a four degrees of freedom (4-DoF) (surge, sway, roll, and yaw) maneuvering motion model is studied in this paper. A time-scale decomposition method is introduced to solve the path-following problem, implementing Rudder Roll Stabilization (RRS) at the same time. The control objectives are to let the ship to track a predefined curve path under environmental disturbances, and to reduce the roll motion at the same time. A singular perturbation method is used to decouple the whole system into two subsystems of different time scales: the slow path-following subsystem and the fast roll reduction subsystem. The coupling effect of the two subsystems is also considered in this framework of analysis. RRS control is only possible when there is the so-called bandwidth separation characteristic in the ship motion system, which requires a large bandwidth separation gap between the two subsystems. To avoid the slow subsystem being affected by the wave disturbances of high frequency and large system uncertainties, the L1 adaptive control is introduced in the slow subsystem, while a Proportion-Differentiation (PD) control law is adopted in the fast roll reduction subsystem. Simulation results show the effectiveness and robustness of the proposed control strategy.